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To know about the placement of pillars of bridges or any structures on the river bank, one must have an idea about coffer dams. A coffer dam is a type of temporary dam; Which prevents water from entering rivers, lakes etc. during construction. Some of the water seeps through the coffer dam, which can easily be pumped out. Coffer dams are mainly installed to keep the construction area dry.
The walls of the coffer dam are waterproof. Coffer dams are classified depending on the type of construction work. The type of construction work depends on the depth, soil condition, water level fluctuation, availability of material etc. Coffer dams are constructed of earthen, wooden or steel sheet piles or a combination thereof.
Coffer dams are used for several purposes; such as
To prevent water ingress into enclosures.
To provide platforms for workers to work on laying foundations in water.
Provides space for foundation by leaving adjacent structures free without reaction.
Facilitates pile placement.
Blatt and grillage help lay the foundation
Concrete helps in carrying out foundation and superstructure works of dams.
Facilitates construction of foundations for bridge abutments and piers.
Types of Coffer Dam:
Where coffer dams are placed, the silt is first removed by dredging. Then the pile has to be setup. After all, the water inside the coffer dam is drained by pumping and it is ensured that water does not seep in from outside. Then the work of making the structure or pillars is started. After the work, the coffer dam is carefully removed.
Coffer dams are constructed using a variety of materials (eg, seat files, steels). Coffer dams are of different types based on the material used, viz
Earth coffer dam
Rock-fill Coffer Dam
Sand bag coffer dam
Single wall coffer dam
Double wall coffer dam
Rock-fill crib coffer dam
Concrete coffer dam
*Cellular Coffer Dam
Cantilever sheet pile coffer dam
Braced Coffer Dam
Suspended Coffer Dam
Earth coffer dams are the most common and known. Where the water depth is about 2 m and the flow velocity is low, earth coffer dams are used.
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